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Subject: Re: [patch 00/17] CFS Bandwidth Control v7.1
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>, Paul Turner <pjt@google.com>,
        linux-kernel@vger.kernel.org,
        Bharata B Rao <bharata@linux.vnet.ibm.com>,
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        Pavel Emelyanov <xemul@openvz.org>, Hu Tao <hutao@cn.fujitsu.com>
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References: <20110707053036.173186930@google.com>
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Date: Thu, 07 Jul 2011 19:08:57 +0200
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On Thu, 2011-07-07 at 09:52 -0700, Andi Kleen wrote:
> Peter Zijlstra <a.p.zijlstra@chello.nl> writes:
> >
> > +static void account_cfs_rq_runtime(struct cfs_rq *cfs_rq,
> > +               unsigned long delta_exec)
> > +{
> > +       if (!cfs_rq->runtime_enabled)
> > +               return;
> > +
> > +       cfs_rq->runtime_remaining -= delta_exec;
> > +       if (cfs_rq->runtime_remaining > 0)
> > +               return;
> > +
> > +       assign_cfs_rq_runtime(cfs_rq);
> > +}
> >
> > generate a call, only to then take the first branch out, marking that
> 
> You would need a *LOT* of calls to make up for 9%.
> 
> Maybe it's something else? Some profiling first before optimization
> is probably a good idea.

This is the 1.5% case where the feature is compiled in but not used.